Lymphokines, substances elaborated by antigenically or mitogenically stimulated lymphocytes, include mediators that alter the physiology of macrophages. In this category is migration inhibitory factor (MIF), a factor which inhibits the migration of macrophages in vitro, exhibits colony stimulating activity on cultured human bone marrow cells and is capable of differentiating HL 60 cells. Another macrophage directed lymphokine is antileishmanial MAF which activates macrophages to kill the intracellular parasite Leishmania donovani. The proposed work aims to establish the basis for the heterogeneity of MIF. We further intend to structurally compare these species of MIF to antileishmanial MAF. We have found that lymphocytes stimulated with tetanus toxoid for two days produce only pH5-MIF, whereas lymphocytes stimulated with Candida antigen produce only pH3-MIF. The planned approach is to first investigate the cellular origin and the functional differences of different antigen dependent species of MIF. We will determine whether each MIF species has additional distinct activities. We will then undertake construction of human T-cell hybridomas with antigen stimulated pure T4+ and T8+ cells as a source of an individual species of lymphokines. Molecular cloning of human MIF species and subsequently of human antileishmanial MAF will be performed in order to be able to isolate clones of cDNA encoding these lymphokines. The availability of lymphokine clones will enable us to ask the question whether heterogeneity of MIF is based on the action of different genes or on post transcriptional modification.